The Network Time Protocol (NTP) is used to synchronize the time of a computer client or server to another server or reference time source, such as a radio or satellite receiver or modem. It provides client accuracies typically within a millisecond on LANs and up to a few tens of milliseconds on WANs relative to a primary server synchronized to Coordinated Universal Time (UTC) via a Global Positioning Service (GPS) receiver, for example.

BobChess is a simple online chess clock with Normal, Fischer, Simple Delay, and Bronstein modes. It runs entirely in your browser using trivial JavaScript. Everything is contained in one file, so it is possible to easily download a version to use offline.

xarclock is an extension of the standard X clock widget. It adds the option to display three lines at the bottom of the clock with the contents of the file /tmp/xarclock.txt. Numbers on the clock face have font support. Direction of rotation is configurable.

daytime is a program that can get the current time from "daytime" (RFC-867), "time" (rfc-868), "nist daytime", or HTTP servers. It only uses the TCP versions of these protocols. It can set the system or hardware clocks from the retrieved time.

Screwdriver++ is a package with various tools for the C++ programmer in Unix environments. It contains classes for time measurement, image and file manipulation, and arbitrary precision arithmetics. Timer is a class for measuring time intervals with millisecond accuracy. Image is a class that uses OpenCv to manipulate images. File is a class to manipilate file input and output in various formats. Number is a class to manipulate arbitrary precision arithmetics.

Gameclock is a fairly simple application designed to track the time spent thinking by the players during a chess game. Various clock engines are available (speed chess, fisher chess, board games, or hourglass). The graphical interface is keyboard-driven and is intended to be minimal and simple. The code is made to be extensible to other game types.

WMTime is a Window Maker dock app that displays the time and date and gives you some nice additional features too. It provides a realtime morphing interface (analog <> digital mode), auto-scaled and anti-aliased hands, localization that displays the day and date in various languages, and three user-defined launch commands.